It has been demonstrated that carcinogenesis in a number of tissues and species can be divided into two stages, initiation and promotion. Furthermore, studies have shown that the stages involved in carcinogenesis are often accompanied by gene activation and/or altered patterns of gene expression. This research proposal will determine the respective roles played by skin tumor initiators and promoters in bringing about altered gene expression at various times during two-stage carcinogenesis in mouse skin. The proposed studies will examine the effects of polycyclic aromatic hydrocarbon initiation with benzo(a)pyrene diol epoxides and repetitive treatments with the skin tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) on the expression of specific genes in epidermis of the SENCAR mouse, a skin tumor-sensitive strain. For this purpose we will analyze several categories of well-characterized murine sequences which have been previously implicated in carcinogenesis. These include the endogenous proviral sequences of murine leukemia virus (MuLV), long terminal repeats (LTRs), and a panel of oncogenes. All of these DNA sequences are available as molecular clones, thus facilitating detection of altered patterns of gene expression and gene rearrangement. Levels of gene transcripts in normal epidermis and epidermis treated with initiator and/or promoter will be compared by RNA blot hybridization analysis to levels in papillomas and squamous cells carcinomas. Immunospecific probes for specific proteins expressed by these groups of sequences will be used to study induction and/or alteration of translation at various stages of carcinogenesis. Restriction analysis of genomic DNA by Southern blot hybridization methods will be used to screen DNA purified from epidermis and tumors at various times during carcinogenesis for evidence of gene rearrangements. With this approach we hope to establish whether activation or altered patterns of gene expression in skin during two-stage carcinogenesis coincide with particular stages of carcinogenesis and tumor development. The proposed studies will contribute to our knowledge of the respective roles played by carcinogenic initiators and skin promoters in the induction of altered gene expression in skin at various stages of tumorigenesis.